It is considered desirable to apply fluids and coatings to a moving web substrate from a rotating device. The selective transfer of such fluids and coatings for purposes such as printing is also desirable. Further, the selective transfer of a fluid to a surface by way of a permeable element is also desirable.
For example, screen printing provides for the transfer of a fluid to a surface through a permeable element. The design transferred in screen printing is formed by selectively occluding openings in the screen that are located according to the formation of the screen. The aspect ratio of the holes and fluid viscosity may limit the fluid types, application rate, or fluid dose that may be applied with screen printing.
Other fluid application efforts have utilized sintered metal surfaces as transfer elements. A pattern of permeability has been formed using the pores in the element. These pores may be generally closed by plating the material and then selectively reopened by machining a desired pattern upon the material and subsequently chemically etching the machined portions of the element to reveal the existing pores. In this manner a pattern of permeability corresponding to the pores initially formed in the material may be formed and used to selectively transfer fluid. The nature of the pores in a sintered material is generally so the tortuosity of the pores predisposes the pores to clogging by fluid impurities. The placement of the fluid is limited in the prior art to the pores or openings present in the material that may be selectively closed or generally closed and selectively reopened.
Gravure printing is also provides a method for transferring fluid to the surface of a moving web material. The use of fixed volume cells engraved onto the surface of a print cylinder can ensure high quality and consistency of fluid transfer over long run times. However, a given cylinder is limited in the range of flow rates possible per unit area of web surface.
Additional efforts directed toward a ‘gravure-like’ system have focused on the use of a roll having discrete cells disposed upon an outer surface. Each cell of the discrete cells receives a fluid from a position internal to the roll. Generally, the fluid is provided to the discrete cells by a channel disposed internally to the roll. These channels are usually provided parallel to the axis of rotation of the roll and are disposed in a region proximate to the axis of rotation of the roll. One reason for this arrangement is that one of skill in the art generally feeds fluids into a rotating device at a position near the axis of rotation. This provides the ability to incorporate such fluid feeds into the shaft that supports the rotating device.
Additionally, it is understood that generally, high rotational (line) speeds are considered by those of skill in the art as highly desirable for increased production rates. However, it was found that when current rotary systems, such as the exemplary gravure printing system described supra, are filled with a fluid and rotate at a high circumferential speed, the centrifugal force was found to create a region(s) of low pressure (i.e., “pull a vacuum”) in the fluid channels, or those portions of the fluid channels, that are disposed in regions proximate to the axis of rotation of the rotating device. This region of low pressure is thought to provide three undesirable phenomena in operations where high rotational velocities are required:    1. When the rotating device reaches a certain rotational speed, the local pressure in any channel, or portion(s) thereof, disposed within the rotating device that are proximate to the axis of rotation is reduced below the vaporization pressure of the fluid at the local temperature. The fluid is caused to vaporize and form gas bubbles. This phenomenon can be considered to be analogous to the cavitation observed in a hydraulic pump operating at high rpm.    2. If the fluid is not deaerated properly, the size of any entrained air bubbles in the fluid will increase as the pressure drops.    3. According to Henry's law, the amount of air dissolved in a fluid is proportional to the local pressure. When a fluid transported from a position external to the rotary device to the center of the rotary device through a channel disposed within the rotating device, the pressure exerted upon the fluid changes from atmospheric to a near vacuum. Part of this dissolved air can then be released in the form of bubbles in the fluid.
According to the ideal gas law, the gas or air bubble volume is inversely proportional to the local pressure. Therefore, the size of bubbles within the fluid will increase as the rotational speed increases. This is because the pressure in any fluid channels, or portions thereof, located in the region near the rotational axis decreases as the rotational speed increases. These gas or air bubbles introduce difficulties in high rotational speed operations, such as printing and coating. These can include undesirable flowrates, partial blockages within the internal roll piping, noise, vibration, and damage to the piping network. The latter can be considered analogous to the damage due to cavitation caused by an impeller.
Thus, one of skill in the art will recognize that such undesired phenomena caused by these centrifugal forces, such as those described supra, must be controlled to enhance the speed and performance of equipment used in material processing technologies. A design that controls and increases the performance of high-speed rotary unions is needed in manufacturing. Clearly, a design that can correlate equipment design, fluid dynamics, and high-speed manufacturing is needed.
The rotary device of the present disclosure overcomes these problems associated with the prior art by providing a rotary device for use in a fluid delivery system that is capable of transporting single or multiple fluids and controlling the pressure drop due to high-speed rotation of internally-fed rolls at the fluid inputs, and prevents the creation of a region(s) of low pressure in an economical manner. The disclosed rotary device can be modified to accommodate different numbers of flow channels and is designed to ensure efficient rotation between incoming and outgoing conduit arrangements.